Robert F. Shepherd's research while affiliated with Cornell University and other places
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Publications (144)
Triply periodic minimal surface lattices have mechanical properties that derive from the unit cell geometry and the base material. Through computation software like nTopology and Abaqus, these geometries are used to tune nonlinear stress–strain curves not readily achievable with solid materials alone and to change the compliance by two orders of ma...
As an alternative approach to ionic data transmission with hydrogel as substrate, this work explores the possible applications of liquid electrolyte filling cavity of a stretchable, flexible elastomeric tubing, which is the primary ingredient used in redox flow battery systems. While hydrogel-based ionic impedance characterization and its data comm...
Fluid‐Driven Elastomer Actuators In article number 2200330, Kirstin H. Petersen and co‐workers present fluidic actuators in which viscous fluids propagate in a scalable framework manifesting control of the structure by the structure, generating pressure distributions within each actuator ‐ achieving interchangeable, spatio‐temporal motions with a s...
Herein, complex motion in soft, fluid‐driven actuators composed of elastomer bladders arranged around a neutral plane and connected by slender tubes is demonstrated. Rather than relying on complex feedback control or multiple inputs, the motion is generated with a single pressure input, leveraging viscous flows within the actuator to produce nonuni...
Aeronautics research has continually sought to achieve the adaptability and morphing performance of avian wings, but in practice, wings of all scales continue to use the same hinged control-surface embodiment. Recent research into compliant and bio-inspired mechanisms for morphing wings and control surfaces has indicated promising results, though o...
Aeronautics research has continually sought to achieve the adaptability and morphing performance of avian wings, but in practice, wings of all scales continue to use the same hinged control-surface embodiment. Recent research into compliant and bio-inspired mechanisms for morphing wings and control surfaces has indicated promising results, though o...
We introduce damage intelligent soft-bodied systems via a network of self-healing light guides for dynamic sensing (SHeaLDS). Exploiting the intrinsic damage resilience of light propagation in an optical waveguide, in combination with a tough, transparent, and autonomously self-healing polyurethane urea elastomer, SHeaLDS enables damage resilient a...
This work reports a three-dimensional polymer interdigitated pillar electrostatic actuator that can produce force densities 5–10× higher than those of biological muscles. The theory of operation, scaling, and stability is investigated using analytical and FEM models. The actuator consists of two high-density arrays of interdigitated pillars that wo...
We present formulation and open-source tools to achieve in-material model predictive control of sensor/actuator systems using learned forward kinematics and on-device computation. Microcontroller units that compute the prediction and control task while colocated with the sensors and actuators enable in-material untethered behaviors. In this approac...
We use magnetohydrodynamic levitation as a means to create a soft, elastomeric, solenoid-driven pump (ESP). We present a theoretical framework and fabrication of a pump designed to address the unique challenges of soft robotics, maintaining pumping performance under deformation. Using a permanent magnet as a piston and ferrofluid as a liquid seal,...
Conventional strain gauges are not designed for accurate measurement over the large range of deformations possible in compliant textiles. The thin, lightweight, and flexible nature of textiles also makes it challenging to attach strain gauges in a way that does not affect the mechanical properties. In this manuscript, soft, highly extensible fibers...
Collagen is the most abundant component of mammalian extracellular matrices. As such, the development of materials that mimic the biological and mechanical properties of collagenous tissues is an enduring goal of the biomaterials community. Despite the development of molded and 3D printed collagen hydrogel platforms, their use as biomaterials and t...
Flexible hybrid electronic (FHE) materials and devices exploit the interaction of mechanical and electromagnetic properties to operate in new form factors and loading environments, which are key for advancing wearable sensors, flexible antennas, and soft robotic skin technologies. Dielectric elastomer (DE) architectures offer a novel substrate mate...
Flesh encodes a variety of haptic information including deformation, temperature, vibration, and damage stimuli using a multisensory array of mechanoreceptors distributed on the surface of the human body. Currently, soft sensors are capable of detecting some haptic stimuli, but whole-body multimodal perception at scales similar to a human adult (su...
Objective
To develop a novel in vitro method for evaluating coronary artery ischemia using a combination of non-invasive coronary CT angiograms (CCTA) and 3D printing (FFR 3D ).
Methods
Twenty eight patients with varying degrees of coronary artery disease who underwent non-invasive CCTA scans and invasive fractional flow reserve (FFR) of their epi...
We present a suite of algorithms and tools for model-predictive control of sensor/actuator systems with embedded microcontroller units (MCU). These MCUs can be colocated with sensors and actuators, thereby enabling a new class of smart composites capable of autonomous behavior that does not require an external computer. In this approach, kinematics...
Elastomer‐granule composites have been used to switch between soft and stiff states by applying negative pressure differentials that cause the membrane to squeeze the internal grains, inducing dilation and jamming. Applications of this phenomenon have ranged from universal gripping to adaptive mobility. Previously, the combination of this jamming p...
Autonomous robots comprise actuation, energy, sensory and control systems built from materials and structures that are not necessarily designed and integrated for multifunctionality. Yet, animals and other organisms that robots strive to emulate contain highly sophisticated and interconnected systems at all organizational levels, which allow multip...
An acoustic liquefaction approach to enhance the flow of yield stress fluids during digital light processing (DLP) based 3D printing is reported. This enhanced flow enables processing of ultrahigh viscosity resins (μapp > 3700 Pa·s at shear rates γ = 0.01 s–1) based on silica particles in a silicone photopolymer. Numerical simulations of the acoust...
Flexible and shape-shifting structures are common in nature. Creating shape-shifting machines using rigid components requires complex design work. Soft robotic attempts are closer to the muscular hydrostats they mimic but are slow and inefficient untethered and do not generally allow large-scale shape change between forms. Here we present the idea...
New classes of functional soft materials show promise to revolutionize robotics. Now materials scientists must focus on realizing the predicted performance of these materials and developing effective and robust interfaces to integrate them into highly functional robotic systems that have a positive impact on human life.
Significance
Even in the rapidly accelerating digital age, the portable, electronic tactile display remains an unsolved actuation technology challenge. The design requirements associated with manufacturing arrays of closely spaced, small actuators are notoriously difficult to satisfy, shown by how currently available actuation strategies fail when...
Artificial muscles based on stimuli-responsive polymers usually exhibit mechanical compliance, versatility, and high power-to-weight ratio, showing great promise to potentially replace conventional rigid motors for next-generation soft robots, wearable electronics, and biomedical devices. In particular, thermomechanical liquid crystal elasto-mers (...
SmartSuit is an advanced planetary spacesuit for the next generation of exploration missions that capitalizes on a novel architecture to improve on current gas-pressurized spacesuits. The SmartSuit, while gas-pressurized, also incorporates the following three technological innovations: 1) a full-body soft-robotic layer inside the gas-pressurized su...
INTRODUCTION: Current spacesuits are cumbersome and metabolically expensive. The use of robotic actuators could improve extravehicular activity performance. We propose a novel method to quantify the benefit of robotic actuators during planetary ambulation. METHODS: Using the OpenSim framework, we completed a biomechanical analysis of three walking...
Since the modern concepts for virtual and augmented reality are first introduced in the 1960's, the field has strived to develop technologies for immersive user experience in a fully or partially virtual environment. Despite the great progress in visual and auditory technologies, haptics has seen much slower technological advances. The challenge is...
Despite the promise of operation in extreme environments and the use of high energy density power sources, strategies for thermoregulation remain underdeveloped in soft robots. Here, we present autonomically perspiring fluidic actuators based on multimaterial 3D printing of smart-gels. We developed two custom hydrogel photochemistries—one based on...
Robots have been built to accomplish specific tasks with high repeatability instead of general utility. Taking inspiration from the evolution of animals to survive and adapt to changing environments, we discuss how a bottom up approach that begins with new materials could lead to robots that may address needs for autonomy and general utility across...
We present a high-bandwidth, lightweight, and nonlinear output tracking technique for soft actuators that combines parsimonious recursive layers for forward output predictions and online optimization using Newton-Raphson. This technique allows for reduced model sizes and increased control loop frequencies when compared with conventional RNN models....
To mitigate the adverse effects of elevated temperatures, conventional rigid devices use bulky radiators, heat sinks and fans to dissipate heat from sensitive components. Unfortunately, these thermoregulation strategies are incompatible with soft robots, a growing field of technology that, like biology, builds compliant and highly deformable bodies...
We present a high-bandwidth, lightweight, and nonlinear output tracking technique for soft actuators that combines parsimonious recursive layers for forward output predictions and online optimization using Newton-Raphson. This technique allows for reduced model sizes and increased control loop frequencies when compared with conventional RNN models....
A 3D-printing technique has been developed that can produce millimetre- to centimetre-scale objects with micrometre-scale features. It relies on chemical reactions triggered by the intersection of two light beams. Polymerization at intersecting light beams enables rapid 3D printing.
Background: Virtual functional assessment index (vFAI), an alternative approach for assessing hemodynamic significance of stenosis has been shown to enhance the diagnostic performance of coronary computed tomography angiography (CCTA) based on evaluating the area under pressure drop-flow curve for a stenosis. Previously, this was assessed via compu...
Colorful changes
Distributed fiber-optic sensors have been used for monitoring mechanical deformations in stiff infrastructures such as bridges, roads, and buildings, but they either are limited to measuring one variable or require complex optics to measure multiple properties. Bai et al. now demonstrate dual-core elastomeric optical fibers, one of...
In article number 2005244, Robert F. Shepherd and co‐workers introduce a comprehensive multi‐material system and fabrication route for the design and manufacture of soft, electrohydraulic actuators. The actuation and self‐sensing capabilities of the capacitive modules are demonstrated. Moreover, they employ 3D printing to pattern dense arrays of th...
A comprehensive material system is introduced for the additive manufacturing of electrohydraulic (HASEL) tentacle actuators. This material system consists of a photo‐curable, elastomeric silicone‐urethane with relatively strong dielectric properties (εr ≈ 8.8 at 1 kHz) in combination with ionically‐conductive hydrogel and silver paint electrodes th...
Additive manufacturing permits innovative soft device architectures with micron resolution. The processing requirements, however, restrict the available materials, and joining chemically dissimilar components remains a challenge. Here we report silicone double networks (SilDNs) that participate in orthogonal crosslinking mechanisms—photocurable thi...
The rheological parameters required to print viscoelastic nanoparticle suspensions toward tough elastomers via Digital Light Synthesis (DLS) (an inverted projection stereolithography system) are reported. With a model material of functionalized silica nanoparticles suspended in a poly(dimethylsiloxane) matrix, the rheological‐parameters‐guided DLS...
The "SmartSuit" is a novel spacesuit intelligent architecture for extravehicular activity (EVA) operations on Mars and other planetary environments that increases human performance by an order of magnitude on several quantifiable fronts for exploration missions. The SmartSuit spacesuit, while gas-pressurized, also incorporates soft-robotics technol...
This work addresses the challenge of underactuated pattern generation in continuous multistable structures. The examined configuration is a slender membrane which can concurrently sustain two different equilibria states, separated by transition regions, and is actuated by a viscous fluid. We first demonstrate the formation and motion of a single tr...
Stretchable optoelectronic materials are essential for applications in wearable electronics, human–machine interfaces and soft robots. However, intrinsically stretchable optoelectronic devices such as light-emitting capacitors usually require high driving alternating voltages and excitation frequencies to achieve sufficient luminance in ambient lig...
In both biological and engineered systems, functioning at peak power output for prolonged periods of time requires thermoregulation. Here, we report a soft hydrogel-based actuator that can maintain stable body temperatures via autonomic perspiration. Using multimaterial stereolithography, we three-dimensionally print finger-like fluidic elastomer a...
We propose a novel spacesuit intelligent architecture for extravehicular activity (EVA) operations on Mars and other planetary environments that increases human performance by an order of magnitude on several quantifiable fronts for exploration missions. The proposed SmartSuit spacesuit, while gas-pressurized, also incorporates soft-robotics techno...
Whereas vision dominates sensing in robots, animals with limited vision deftly navigate their environment using other forms of perception, such as touch. Efforts have been made to apply artificial skins with tactile sensing to robots for similarly sophisticated mobile and manipulative skills. The ability to functionally mimic the afferent sensory n...
This article presents a machine learning approach to map outputs from an embedded array of sensors distributed throughout a deformable body to continuous and discrete virtual states, and its application to interpret human touch in soft interfaces. We integrate stretchable capacitors into a rubber membrane, and use a passive addressing scheme to pro...
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Current efforts to improve building envelopes mostly focus on reducing energy demand by static measures such as insulation, selective glazing and shading. The resulting envelopes are limited in adapting to weather conditions or occupants’ needs and leave vast potentials for energy savings, onsite energy generation and improvement of occupant comfor...
Modern robots lack the multifunctional interconnected systems found in living organisms and are consequently unable to reproduce their efficiency and autonomy. Energy-storage systems are among the most crucial limitations to robot autonomy, but their size, weight, material and design constraints can be re-examined in the context of multifunctional,...
Inspired by nature, we herein demonstrate a family of multi-responsive hydrogel-based actuators that are encoded with anisotropic swelling behavior to provide rapid and controllable motion. Fabrication of the proposed anisotropy-encoded hydrogel actuators relies on the high resolution stereolithography 3D printing of functionally graded structures...
This paper reports the rapid 3D printing of tough (toughness, UT, up to 141.6 kJ m⁻³), highly solvated (Φwater~60 v/o), and antifouling hybrid hydrogels for potential uses in biomedical, smart materials, and sensor applications, using a zwitterionic photochemistry compatible with stereolithography (SLA). A Design of Experiments (DOE) framework was...
Soft materials possess several distinctive characteristics like controllable deformation, infinite degrees of freedom, and self‐assembly that make them promising candidates for building soft machines, robots, and haptic interfaces. In this article, we review recent advances in intrinsically soft materials, and soft‐material‐enabled robots, machines...
Front Cover: Photomechanical polymeric materials could be the future for building light‐driven soft robotic actuators. In article number 1800815, Robert F. Shepherd and co‐workers propose a simple synthesis and processing route for the fabrication of a self‐healing photomechanical elastomer. This material enables the construction of complex 3D shap...
Soft materials possess several distinctive characteristics like controllable deformation, infinite degrees of freedom, and self‐assembly that make them promising candidates for building soft machines, robots, and haptic interfaces. In this article, we review recent advances in intrinsically soft materials, and soft‐material‐enabled robots, machines...
This article introduces a simple two‐stage method to synthesize and program a photomechanical elastomer (PME) for light‐driven artificial muscle‐like actuations in soft robotics. First, photochromic azobenzene molecules are covalently attached to a polyurethane backbone via a two‐part step‐growth polymerization. Next, mechanical alignment is applie...
Although physical buttons provide tactile sensations that allow them to be identified and pressed without visual focus, their static nature limits their use for dynamic interfaces. Conversely, touchscreens offer highly flexible, task-specific interfaces, but they do not provide the tactile qualities needed for vision-free interaction. Here, we pres...
Virtual reality experiences via immersive optics and sound are becoming ubiquitous; there are several consumer systems (e.g., Oculus Rift and HTC Vive) now available with these capabilities. Other sensory experiences, such as that of touch remain elusive in this field. The most successful examples of haptic sensation (e.g., Nintendo 64's Rumble Pac...
In a step toward soft robot proprioception, and therefore better control, this paper presents an internally illuminated elastomer foam that has been trained to detect its own deformation through machine learning techniques. Optical fibers transmitted light into the foam and simultaneously received diffuse waves from internal reflection. The diffuse...
The force, speed, dexterity, and compact size required of prosthetic hands present extreme design challenges for engineers. Current prosthetics rely on high-quality motors to achieve adequate precision, force, and speed in a small enough form factor with the trade-off of high cost. We present a simple, compact, and cost-effective continuously varia...
Natural organisms use a combination of contracting muscles and inextensible fibers to transform into controllable shapes, camouflage into their surrounding environment, and catch prey. Replicating these capabilities with engineered materials is challenging because of the difficulty in manufacturing and controlling soft material actuators with embed...
Advancements in 3D additive manufacturing have spurred the development of effective patient‐specific medical devices. Prior applications are limited to hard materials, however, with few implementations of soft devices that better match the properties of natural tissue. This paper introduces a rapid, low cost, and scalable process for fabricating so...
Soft robots are capable of mimicking the complex motion of animals. Soft robotic systems are defined by their compliance, which allows for continuous and often responsive localized deformation. These features make soft robots especially interesting for integration with human tissues, for example, the implementation of biomedical devices, and for ro...
Combustion in soft and compliant materials may enable new methods for underwater locomotion. Inspired by the motion of the soft bodied cephalopods, we developed a combustion-powered hydro-jet engine (CPHJE) using an expandable silicone bladder. The CPHJE used high energy density methane combustion to expand a silicone bladder and accelerate water i...
Systems and methods for providing a soft robot is provided. In one system , a robotic device includes a flexible body having a fluid chamber, where a portion of the flexible body includes an elastically extensible material and a portion of the flexible body is strain limiting relative to the elastically extensible material. The robotic device can f...
Some embodiments of the disclosed subject matter includes a laminated robotic actuator. The laminated robotic actuator includes a strain-limiting layer comprising a flexible, non extensible material in the form of a sheet or thin film, a flexible inflatable layer in the form of a thin film or sheet in facing relationship with the strain-limiting la...
Systems and methods for providing flexible robotic actuators are disclosed. Some embodiments of the disclosed subject matter include a soft robot capable of providing a radial deflection motions; a soft tentacle actuator capable of providing a variety of motions and providing transportation means for various types of materials; and a hybrid robotic...
3D printing has been used to create a wide variety of anatomical models and tools for procedural planning and training. Yet, the printing of permanent, soft endocardial implants remains challenging because of the need for haemocompatibility and durability of the printed materials. Here, we describe an approach for the rapid prototyping of patient-s...